A simple pre-filtering for spectral smoothing in a radio frequency digital to analog converter

A new pre-filtering scheme for direct digital to RF converter is presented. The converter consists of a 400MS/s digital ΣΔ modulator followed by a 2.4-GHz digital to Radio Frequency (RF) converter. The proposed structure attenuates the out-of-band spectral and relaxes the design of ΣΔ and RF-Filter. The technique is based on using First Order Hold filter in respect to use the conventional Zero Order Hold filter. The simulation result shows 16dB image rejection improvement. Also, the modulator achieved 79dB of Signal to Noise Ratio in 5MHz of band width. The output power is -4dBm while power consumption is about 2.55mW.